1. Technical Field
The present invention relates to improvements in a recirculating bearing assembly and an improved method of making such a bearing assembly. In particular, the present invention is directed to a linear recirculating bearing of the type having reduced skewing or forces in a direction perpendicular to the direction of bearing assembly movement.
2. Background Art
Various recirculating bearing assemblies are known in the prior art. One such system is shown in U.S. Pat No. 3,758,176 issued to Stapley and assigned to Sundstrand Corporation. The bearing assembly disclosed in that patent utilizes a central body having a cross-shaped cross section with roller elements in rolling engagement on both top and bottom of a horizontal cross member. Separate end caps at each end of this cross shaped body provide a roller return.
While the bearing shown in the Stapley patent is generally acceptable for most roller bearing application in terms of performance, several manufacturing challenges and resulting costs are inherent in the design. For example, the horizontal left and right portions of the cross on upper and lower surfaces must be machined to a high degree of flatness, parallelism and a uniform dimension between sides, but the intermediate vertical cross piece prevents machining as a single element in a single pass. Additionally, the separate manufacture of a pair of endcaps for each bearing requires manufacture and inventory of additional parts which, in the patent's design, are of different materials. This requires inventory and assembly costs. A similar bearing is shown in U.S. Pat. No. 3,608,985 issued to Swanson.
Other recirculating bearing designs are shown in U.S. Pat. Nos. 3,003,828 to Stark and 3,341,262 to Kalmanek which relate generally to linear recirculating bearings having a plurality of dumbbell-shaped roller elements in a single race. This type of recirculating bearing has a generally favorable performance characteristics. However, this bearing exhibits a certain amount of inherent skewing and resistance to rolling in the linear direction. This bearing is also relatively expensive to manufacture, based partially on the cost for the unconventionally-shaped rollers and the tolerances required.
Additionally, the dumbbell portions of the rollers must be uniform to a high degree both between the two ends and one to another in order to minimize skewing and resistance to rolling.
Many other examples of linear recirculating bearing assemblies are known in the prior art. Examples of such bearings are shown, for example, in U.S. Pat. Nos. 3,101,978 and 3,241,890. In such bearings, there are significant limitations either in the bearing cost or performance or ease of manufacture, or some combinations thereof.
Accordingly, bearing assemblies of the prior art have limitations, both in terms of performance and manufacturing costs. One key limitation in performance is the amount of skewing, or forces perpendicular to the axis of bearing movement, which the bearing exhibits when moved along its direction of movement.